Urinary System

Urinary Bladder - Metaplasia

Narrative
Comment:
Metaplasia of the urothelium reflects the potential of the urothelium to undergo a metaplastic change under a variety of conditions. Squamous metaplasia, with or without keratinization, is the most common variant observed (Figure 1, Figure 2, and Figure 3). Mucinous, glandular, or mixtures of metaplastic lesions are less commonly observed (Figure 4).
Recommendations:
Urothelial metaplasia and, in particular, the type of metaplasia should be diagnosed and given a severity grade when it becomes a major part of a lesion, for instance, in association with inflammation or hyperplasia. Small or focal lesions, when part of a primary lesion such as chronic inflammation and/or hyperplasia, should not be diagnosed separately.
References:

Gaillard ET. 1999. Ureter, urinary bladder and urethra. In: Pathology of the Mouse: Reference and Atlas (Maronpot RR, Boorman GA Gaul BW, eds). Cache River Press, Vienna, IL, 235-258.

Abstract: http://www.cacheriverpress.com/books/pathmouse.htm

Jokinen MP. 1990. Urinary bladder, ureter, and urethra. In: Pathology of the Fischer Rat: Reference and Atlas (Boorman GA, Eustis SL, Elwell MR, Montgomery CA, MacKenzie WF, eds). Academic Press, San Diego, 109-126.

Abstract: http://www.ncbi.nlm.nih.gov/nlmcatalog/9002563
  • Image of metaplasia in the urinary bladder from a female F344/N rat in a chronic study

    Diffuse squamous metaplasia and keratinization of hyperplastic urothelium from a female F344/N rat in a subchronic interim study.

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<p>Diffuse squamous metaplasia and keratinization of hyperplastic urothelium from a female F344/N rat in a subchronic interim study.</p>

Diffuse squamous metaplasia and keratinization of hyperplastic urothelium from a female F344/N rat in a subchronic interim study.
<p>Squamous metaplasia and keratinization from a female F344/N rat in a 40-week interim study.</p>

Squamous metaplasia and keratinization from a female F344/N rat in a 40-week interim study.
<p>Squamous metaplasia with and without keratinization, from a female F344/N rat in a subchronic interim study.</p>

Squamous metaplasia with and without keratinization, from a female F344/N rat in a subchronic interim study.
<p>Mucinous metaplasia (arrows) characterized by mucinous cells in areas of urothelial hyperplasia, from a female F344/N rat in a chronic study.</p>

Mucinous metaplasia (arrows) characterized by mucinous cells in areas of urothelial hyperplasia, from a female F344/N rat in a chronic study.

Authors

John Curtis Seely, DVM, DACVP
Senior Pathologist
Experimental Pathology Laboratories, Inc.
Research Triangle Park, NC

Abraham Nyska,  DVM, Diplomate ECVP, Fellow IATP
Expert in Toxicologic Pathology
Visiting Full Professor of Pathology
Sackler School of Medicine, Tel Aviv University
Timrat Israel

Reviewers

Samuel M Cohen, PHD, MD
Professor
Havlik-Wall Professor of Oncology
Director of Pathology Residency Program
Nebraska Medical Center
Omaha, NE

David E. Malarkey DVM, PhD, DACVP, FIATP
Head, National Toxicology Program Pathology Group
Cellular and Molecular Pathology Branch
Division of the National Toxicology Program
National Institute of Environmental Health Sciences
Research Triangle Park, NC